Re: [Qemu-devel] [PATCH v3 01/12] block: Add op blocker type "device IO"

[Wen Congyang <wency@cn.fujitsu.com>]

On 05/15/2015 02:04 PM, Fam Zheng wrote:
> It blocks device IO.

I am reading mirror codes recently, and have a question:
When block job mirror is finished, the source and target is synced. But we
call bdrv_swap() later(in bh context). Can the guest write something to
the source before the bh is scheduled? If the answer is yes, I think
we should use this to block the guest's disk I/O.

Thanks
Wen Congyang

> 
> All bdrv_op_block_all/blk_op_block_all callers are taken care of:
> 
> - virtio_blk_data_plane_create
> - virtio_scsi_hotplug
> 
>   Device creation, unblock it.
> 
> - bdrv_set_backing_hd
> 
>   Backing hd is not used by device, so blocking is OK.
> 
> - backup_start
> 
>   Blocking target when backup is running, unblock it.
> 
> - mirror_complete
> 
>   Blocking s->to_replace until mirror_exit, OK.
> 
> - block_job_complete
> 
>   The block job may be long running. Unblock it.
> 
> - init_blk_migration
> 
>   The block migration may be long running, Unblock it.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  blockjob.c                      | 1 +
>  hw/block/dataplane/virtio-blk.c | 1 +
>  hw/scsi/virtio-scsi.c           | 1 +
>  include/block/block.h           | 1 +
>  migration/block.c               | 1 +
>  5 files changed, 5 insertions(+)
> 
> diff --git a/blockjob.c b/blockjob.c
> index 2755465..e39bdde 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -51,6 +51,7 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
>                 BlockJobType_lookup[driver->job_type]);
>      bdrv_op_block_all(bs, job->blocker);
>      bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
> +    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, job->blocker);
>  
>      job->driver        = driver;
>      job->bs            = bs;
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 3db139b..3ecc8bd 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -209,6 +209,7 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
>      blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_MIRROR, s->blocker);
>      blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_STREAM, s->blocker);
>      blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_REPLACE, s->blocker);
> +    blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
>  
>      *dataplane = s;
>  }
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index e242fef..5e15fa6 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -772,6 +772,7 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
>              return;
>          }
>          blk_op_block_all(sd->conf.blk, s->blocker);
> +        blk_op_unblock(sd->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
>          aio_context_acquire(s->ctx);
>          blk_set_aio_context(sd->conf.blk, s->ctx);
>          aio_context_release(s->ctx);
> diff --git a/include/block/block.h b/include/block/block.h
> index 7d1a717..906fb31 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -159,6 +159,7 @@ typedef enum BlockOpType {
>      BLOCK_OP_TYPE_RESIZE,
>      BLOCK_OP_TYPE_STREAM,
>      BLOCK_OP_TYPE_REPLACE,
> +    BLOCK_OP_TYPE_DEVICE_IO,
>      BLOCK_OP_TYPE_MAX,
>  } BlockOpType;
>  
> diff --git a/migration/block.c b/migration/block.c
> index ddb59cc..b833bac 100644
> --- a/migration/block.c
> +++ b/migration/block.c
> @@ -379,6 +379,7 @@ static void init_blk_migration(QEMUFile *f)
>          alloc_aio_bitmap(bmds);
>          error_setg(&bmds->blocker, "block device is in use by migration");
>          bdrv_op_block_all(bs, bmds->blocker);
> +        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, bmds->blocker);
>          bdrv_ref(bs);
>  
>          block_mig_state.total_sector_sum += sectors;
>